<p>Numerous studies have examined the cognitive factors influencing the academic achievement of college students, yet the psychological and behavioral factors remain underexplored, particularly in developing countries like Tanzania. Guided by the Broaden-and-Build Theory of Positive Emotions, the Restoration Theory of Sleep, and Self-Regulation Theory, this study explored the association between life satisfaction and academic achievement, the mediating role of sleep quality, and the moderating role of smartphone addiction. Using cross-sectional data from 513 Tanzanian college students, moderated mediation analyses were conducted with SPSS 27 and PROCESS Macro Models 4 and 59, controlling for age, sponsorship status, and occupational status. Results showed that life satisfaction was positively associated with academic achievement and sleep quality, whereas smartphone addiction was negatively associated with all three variables. Sleep quality accounted for a substantial proportion of the association between life satisfaction and academic achievement. Furthermore, smartphone addiction strengthened the association between life satisfaction and sleep quality but weakened the association between sleep quality and academic achievement, while not significantly moderating the direct association between life satisfaction and academic achievement. These findings provide valuable insights into the complex interplay between psychological well-being, sleep health, and digital behavior in a developing-country context, offering both theoretical contributions and practical implications for enhancing student success in higher education.</p>